1. Field
Embodiments of the present invention relate to a ball balancer that corrects dislocation between the center of gravity and a rotation center of a rotator.
2. Description of the Related Art
Conventionally, ball balancers have been known as devices to correct unbalance that causes vibration or noise of a rotary system (dislocation between the center of gravity and a rotation center of a rotator). A typical ball balancer includes a doughnut-shaped race member having an empty space therein, and a plurality of balls movably received within the race member. The ball balancer is concentrically installed to a rotator and is rotated, along with the rotator, about a rotation axis of the rotator. If a rotation speed of the rotator exceeds a resonance rotation speed (i.e. a rotation speed causing primary resonance of a rotary system), the balls move away from a weight unbalance portion of the rotator. This enables correction of unbalance. For example, such a ball balancer is installed to a rotating tub of a washing machine to correct unbalance created by bias of clothes within the rotating tub of the washing machine. In addition to the rotating tub of the washing machine, the ball balancer may be installed to a rotator of a rotary machine, such as a centrifuge or a disc drive.
However, if a rotation speed of the rotator is less than a resonance rotation speed, the balls may move toward the weight unbalance portion of the rotator, rather than moving away from the weight unbalance portion. As a result, unbalance is aggravated. As a countermeasure, Japanese Patent Laid-Open publication No. S54-120957 discloses a balance device in which a plurality of recesses (ball detention positions) are formed in the bottom of the balance device and a tilt angle of inner sidewalls of the recesses is determined such that balance weights (balls) are centrifugally rolled out of the recesses when a dehydrator tub is rotated at a higher rotation speed than a natural frequency of a support system for the dehydrator tub. In the balance device disclosed in the aforementioned publication No. S54-120957, if the rotation speed of the dehydrator tub is greater than the natural frequency, the balance weights are centrifugally separated from the recesses and move to the top of the balance device. If the rotation speed of the dehydrator tub is less than the natural frequency, the balance weights are detained in the recesses, which may restrict aggravation of unbalance.
Japanese Patent Laid-Open publication No. S49-10563 discloses a dehydration/washing machine in which a weight guiding pipe installed to a wash tub is internally provided with a slope, and a weight (ball) is detained in a gap (ball detention position) between the slope and a sidewall opposite to the slope when the wash tub is rotated less than a resonance rotation speed, but centrifugally moves upward along the slope when the wash tub reaches the resonance rotation speed. Also, Japanese Patent Laid-Open publication No. S59-183846 discloses a balancer in which an annular chamber receives liquid and spheres (balls) arranged in the bottom (at ball detention positions) thereof such that the spheres centrifugally move upward from the bottom of the annular chamber along an inclined wall of the annular chamber when a rotating tub is rotated at a higher speed than a resonance point.
However, in the related art, although balls begin to move toward ball detention positions by gravitational force if a rotation speed of a rotator becomes less than a resonance rotation speed (revolutions per minute that cause primary resonance of a rotary system), there is a likelihood that some balls not present at the ball detention positions come into contact with other balls present at the ball detention positions and remain stationary without moving to the ball detention positions. In this case, since gravitational force is applied to the balls not present at the ball detention positions, it may be difficult to move the balls to the ball detention positions. For example, although the aforementioned publication No. S54-120957 describes movement of the balls via vibration of the dehydrator tub, moving the balls not present at the ball detention positions may be impossible because gravitational force applied to the balls is greater than force generated by vibration of the dehydrator tub (i.e. force to move the balls in a peripheral direction of a race member). As such, distributing the balls not present at the ball detention positions in the peripheral direction may be impossible, and therefore increasing a rate of the balls at the ball detention positions may be impossible. This makes it difficult to restrict aggravation of unbalance due to the balls not present at the ball detention positions.